Analysis of cells isolated from retrieved implants. Implants of C57Bl/6 Epo⁺ MSCs in collagen recovered surgically (bottom picture) 15 days following subcutaneous implantation were dissociated with collagenase, and single-cell suspensions were analyzed, as indicated in “Materials and methods,” by flow cytometry, gating on lymphoid subsets on forward and side scatter. The amount of CD4, CD8, NKT, CD19, and NK cells among the host-derived lymphocytes in implants was compared between C57Bl/6 (▪) and Balb/c (□) recipient mice (average of n = 5 per group ± SEM). Filled circle on the right side of arrow indicates C57Bl/6 mouse as recipient, whereas open circle indicates Balb/c mouse as recipient of Epo⁺ C57Bl/6-derived MSCs.